It's just grime, not sure how it's ended up in that pattern though! Maybe where wet stuff has slid down the spokes onto the rim? (Disclaimer: not actual science)
Ah, centrifugal crud.
I do believe that's the technical term, yes.
@AlexD started
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It's just grime, not sure how it's ended up in that pattern though! Maybe where wet stuff has slid down the spokes onto the rim? (Disclaimer: not actual science)